How to get the pixel color values of custom image inside imageview ios?

Question

I know similar question have been asked before.

What I want is to get the RGB pixel value of the Image Inside the Imageview, so it can be any image that pixel values we want to get.

This is what I have used to get the point where the image is clicked.

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];

    if ([touch tapCount] == 2) {
        //self.imageView.image = nil;
        return;
    }

    CGPoint lastPoint = [touch locationInView:self.imageViewGallery];
    NSLog(@"%f",lastPoint.x);
    NSLog(@"%f",lastPoint.y);

} 

And To get the Image I have Pasted this code.

+ (NSArray*)getRGBAsFromImage:(UIImage *)image atX:(int)xx andY:(int)yy count:(int)count
{

 NSMutableArray *result = [NSMutableArray arrayWithCapacity:count];

      /** It requires to get the image into your data buffer, so how can we get the `ImageViewImage` **/

CGImageRef imageRef = [image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = (unsigned char*) calloc(height * width * 4, sizeof(unsigned char));
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, width, height,
                                             bitsPerComponent, bytesPerRow, colorSpace,
                                             kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);

CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);

// Now your rawData contains the image data in the RGBA8888 pixel format.
int byteIndex = (bytesPerRow * yy) + xx * bytesPerPixel;
for (int ii = 0 ; ii < count ; ++ii)
{
    CGFloat red   = (rawData[byteIndex]     * 1.0) / 255.0;
    CGFloat green = (rawData[byteIndex + 1] * 1.0) / 255.0;
    CGFloat blue  = (rawData[byteIndex + 2] * 1.0) / 255.0;
    CGFloat alpha = (rawData[byteIndex + 3] * 1.0) / 255.0;
    byteIndex += 4;

    UIColor *acolor = [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
    [result addObject:acolor];
}

free(rawData);

return result;
}

I am new to ios so please explain and It and suggesting some tutorial will be great.

Answer 1

Use this example article. It is talking about a color picker using images. You can understand required info very easily from it. Helped me in my app. Let me know if any help/suggestion needed ..:)

EDIT:

update your getPixelColorAtLocation: like this. It will give you correct color then.

- (UIColor*) getPixelColorAtLocation:(CGPoint)point {
    UIColor* color = nil;
    CGImageRef inImage = self.image.CGImage;
    // Create off screen bitmap context to draw the image into. Format ARGB is 4 bytes for each pixel: Alpa, Red, Green, Blue
    CGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];
    if (cgctx == NULL) { return nil; /* error */ }

    size_t w = CGImageGetWidth(inImage);
    size_t h = CGImageGetHeight(inImage);
    CGRect rect = {{0,0},{w,h}};
/** Extra Added code for Resized Images ****/
    float xscale = w / self.frame.size.width;
    float yscale = h / self.frame.size.height;
    point.x = point.x * xscale;
    point.y = point.y * yscale;
 /** ****************************************/

/** Extra Code Added for Resolution ***********/
    CGFloat x = 1.0;
    if ([self.image respondsToSelector:@selector(scale)]) x = self.image.scale;
/*********************************************/
    // Draw the image to the bitmap context. Once we draw, the memory 
    // allocated for the context for rendering will then contain the 
    // raw image data in the specified color space.
    CGContextDrawImage(cgctx, rect, inImage); 

    // Now we can get a pointer to the image data associated with the bitmap
    // context.
    unsigned char* data = CGBitmapContextGetData (cgctx);
    if (data != NULL) {
        //offset locates the pixel in the data from x,y. 
        //4 for 4 bytes of data per pixel, w is width of one row of data.
//      int offset = 4*((w*round(point.y))+round(point.x));


        int offset = 4*((w*round(point.y))+round(point.x))*x; //Replacement for Resolution
        int alpha =  data[offset];
        int red = data[offset+1]; 
        int green = data[offset+2]; 
        int blue = data[offset+3]; 
        NSLog(@"offset: %i colors: RGB A %i %i %i  %i",offset,red,green,blue,alpha);
        color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];
    }

    // When finished, release the context
    CGContextRelease(cgctx); 
    // Free image data memory for the context
    if (data) { free(data); }

    return color;
}

Let me know this fix does not work .. :)

Here is the GitHub for my code. Use it to implement picker image. Let me know if more info needed